1, Field of the Invention
The present invention relates to a cellular communication system which comprises a host device, plural subordinate devices, and plural terminals and particularly, to the cellular communication system in which each terminal communicates with the host device through the subordinate device of which the terminal is placed in the service area.
2. Description of the Prior Art
FIG. 3 shows a block diagram showing a conventional cellular communication system. In FIG. 3, reference numeral 101 represents a host device which has four interfaces for communicating with subordinate devices. Reference numerals 102, 103, 104, and 105 represent subordinate devices which are connected with host device 101 through dedicated lines 110, 111, 112 and 113 in a star configuration, respectively. Reference numerals 120 to 125 represent terminals which communicate with host device 101 through subordinate devices 102 to 105.
The cellular communication system is one of data relay systems. In the cellular communication system, host device 101 dynamically assigns one of subordinate devices 102 to 105 to each of terminals 120 to 125 in order to keep communication quality best. For example, host device 101 gives terminal 120 the instruction to communicate through subordinate device 102 when terminal 120 is placed in the service area of subordinate device 102. Host device 101 gives terminal 121 to 125 the similar instructions. Terminals 120 to 125 move across service areas of subordinate devices 102 to 105. Therefore, the number of terminals which are in the service area of each of subordinate devices 102 to 105 fluctuates or the traffic of each of subordinate devices 102 to 105 fluctuates with the lapse of time. Moreover, the numbers of terminals which are in the service areas of subordinate devices 102 to 105 and, therefore, the traffics thereof, are uneven if subordinate devices 102 to 105 are not located at regular intervals. Consequently, the channel capacities of dedicated lines 110 to 113 were determined by the maximum number of terminals which gather in their respective service areas. Heretofore, dedicated lines 110 to 113 had the fixed channel capacities which were determined in such a way.
However, because the channel capacities of dedicated lines 110 to 113 were fixed while the traffics which pass through subordinate devices 102 to 105 are variable, unused channels or unused time slots increased when the traffics decreased. Thus, the channel capacities of dedicated lines 110 to 113 were not used effectively.
In order to overcome the aforementioned disadvantages, the present invention has been made.
An object of the present invention is to provide a cellular communication system in which a host device flexibly changes the channel capacities of lines in accordance with the traffics of subordinate devices, whereby the channel capacities of lines are effectively used even when the system is used under the condition that the traffics fluctuate or are uneven.
According to the invention, there is provided a cellular communication system in which each of terminals communicates with a host device through one of subordinate devices of which the terminal is placed in the service area, wherein the host device and the subordinate devices are connected in series through dedicated lines, the host device determines the channel capacities and corresponding counts of time slots for the subordinate devices in accordance with the traffics of the subordinate devices, the counts of time slots are transmitted from the host device to the subordinate devices through prescribed time slots of the dedicated lines, and the subordinate devices communicate with the host device in the time slots determined by the counts of time slots.
In the above cellular communication system, each subordinate device communicates with the host device in the time slots of the determined count starting from the time slot following the last time slot for the preceding subordinate device.
In the above cellular communication system, the host device determines the counts so that the total of the counts does not exceed the counts of time slots in a frame minus the counts of preoccupied time slots.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of the preferred mode embodiment thereof, as illustrated in the accompanying drawings.